S I L

S IL

( 29 7 )

frequently truncated on the edges or folidangles.

2 . In cubes, either perfect or truncated onthe edges or folid angles.

3- In rhomboidal dodecahedrons.

The cryftals are generally lmali and vari-oufly grouped together. The furface of thecryftals is commonly l'mooth, but fometimesdrufy. Internally it is fliining or gliftening,with a metallic luftre. Its frafture is fmallgrained uneven, fometimes flat conchoidal orimperfe£tly lamellar. It acquires a polifh byfriction., It is foft, confiderably malleable andflexible. Sp. gr. 6.9—7.2.

Before the blow-pipe it melts, parts by de-grees with its fulphur, and affords a bead ofmetallic filver. When expofed to a gentle heatinfufficient for its fufion it becomes coveredwith filaments of metallic filver, as was firftobferved by Schreiber.

It has been analyfed by Klaproth , Sage, andBergman, with the following refults:

Klapr.

Sage.

Berg,

35

— 84 —

75

15

—■ 16 —

25

100

100

IOO

It occurs in veins with quartz, calcareousfpar, heavy fpar, native filver, galena, iron andcopper pyrites, and blende.

The mod fplendid fpecimens of this mineralcome from Mexico , confifting of groupes ofcryftals covered with capillary native filver twoor three inches in length; it is alfo found inPeru ; in the Saxon, Bohemian, Swabian, andHungarian mines, at Kongsberg in Norway ,Schlangenberg in Siberia , and Allemont inFrance .

The tenacity of this mineral is fo great, thatAuguftus, king of Poland , had fomfe medals{truck of it.

Sp. 8. Brittle fulphurated filver. Sproed-glaferz. Wern. Argent vitreux aigre. Broch.

Its colour is iron black, palling into fteel andlead grey. It occurs in mafs, difleminated,membranous, and often cryftallized. Its formsare,

1. The ftrait fix-fided prifm with plane or

convex terminations. When the prifm is veryfitort a fix-fided table is produced: and whentae prifm intervening between the convexfummits is fupprefled the refult is a lenticularcryftal. •

2. A fix-fided prifm terminated by fix-fidedpyramids which are often deeply truncated.

The tabular cryftals often interfea each

VOL. II.

other and thus form cellular groups, Thecryftals are generally very fmall; their furfaceis fometimes fmooth, fometimes drufy, theprifms are ftriated longitudinally. The externalluftre of this mineral is generally very brightlyfhining; internally it varies from gliftering tofhining, with a metallic luftre. Its fraddure isfine grained, uneven, pafling into fmall conchoi-dal. It is foft, brittle, and eafily frangible.Sp. gr. 7.2.

Before the blowpipe, on charcoal, it melts,gives out a white vapour and affords a metallicglobule furrounded by fcorias, but this globuleis not malleable except by fubfequent fufionwith nitre and borax. Its contents, accordingto an analyfis by Klaproth , are,

66.5 Silver10. Antimony5. Iron12. Sulphur0.5 Copper and arfenic1. Earthy impurities

It occurs in veins accompanied by white fil-ver ore (into which it often paffes) ruby filver,galena, rarely cinnabar and gold. It is metwith in Hungary, Tranfilvania, Saxony , Bohe-mia and Swabia, Norway, France, Siberia , dndPeru , but is upon the whole confiderably rarerthan the preceding fpecies.

Sp. 9. Bifmuthic filver. Wifmuthifchesfilber. Epimerl. Argent bifmuthifere. Broch.Its colour is a light lead grey which becomesdeeper by expofure to the air. It occurs gene-rally difleminated, rarely in mafs. Internallyit has a gliftening metallic luftre. Its fractureis fine-grained uneven. It is foft and not verybrittle.

When expofed on charcoal to the blowpipe,metallic globules begin foon to ooze out fromit; on the addition of borax the metallic partscolleft in one mafs, and the flux acquires anamber colour. The metallic button is iridef-cent externally, and tin white internally; it isalfo brittle.

The contents of this ore, according to Klap-roth , are,

33. Lead27. Bifmuth15. Silver4.3 Iron0.9 Copper16.3 Sulphur

9 6 -S

2 P